The reason for the reduced flow is because the filter needs cleaning. Check that the pump is not sitting directly on the pond bed, as this can cause debris and silt to be circulated. Check that there is not an excessive build up of sludge in the pond, if so clean out the pond. Try a different combination of foams e.g. 2 x coarse and 1 x medium instead of coarse, medium and fine. Note with the latest Bioforce range (3000, 5500, 8000 and 12000) these can be cleaned by back flushing without having to remove the lid. Refer to the instruction leaflet.